1. Field of the Invention
This invention relates to a position detecting device for detecting the position of an object, based on an image obtained by an imaging device installed on a vehicle.
2. Description of the Prior Art
Conventionally, a vehicle environment monitoring system has been proposed which detects the position of an object from an image taken by an imaging device carried on a vehicle and determines the possibility of collision between the object and the automotive vehicle. In such a system, since the imaging device is installed on the automotive vehicle which moves or travels, the pitching motion of the vehicle causes optical flow (hereinafter referred to as xe2x80x9cpitching flowxe2x80x9d) to occur in the image obtained by the imaging device fixed to the vehicle. The pitching flow is not caused by a motion of an object (or traveling of the vehicle). Accordingly, when the position of the object is detected from the image taken by the imaging device, deviation of a detected position of the object from the proper position thereof becomes large unless the adverse effects of the pitching flow on the position detection are eliminated.
A possible solution to this problem is that a vehicle height sensor is arranged on the vehicle, for detecting a height of the vehicle (vehicle height) from the road surface, and the detected position of the object is corrected based on the vehicle height detected by the sensor. However, this solution requires the provision of a vehicle height sensor, which leads to complicated construction of the whole system.
It is an object of the invention to provide a position detecting device for a vehicle, which is capable of eliminating the adverse effects of pitching motion of the vehicle on detection of the position of an object, by simple construction thereof, and thereby enabling accurate detection of the position.
To attain the above object, the invention provides a position detecting device for a vehicle, which detects a position of an object in a real space coordinate system, the position detecting device comprising: imaging means installed on the automotive vehicle; correction amount-calculating means for extracting a plurality of objects from an image obtained by the imaging means, and calculating a pitching-dependent correction amount based on amounts of displacement in position of the plurality of objects in a direction of height; and correction means for correcting positions of the plurality of objects based on the pitching-dependent correction amount.
According to this position detecting device, a plurality of objects are extracted from an image obtained by the imaging means, and a pitching-dependent correction amount is calculated based on amounts of displacement in position of the plurality of objects in a direction of height. Positions of the plurality of objects are corrected based on the pitching-dependent correction amount. Therefore, even when displacements of objects in the image in the direction of height are caused by pitching motion of the vehicle, the adverse effects of the displacements can be eliminated by simple construction, without using a vehicle height sensor or the like, thereby ensuring an accurate position detection.
Preferably, the correction amount-calculating means calculates an average value of the amounts of displacement in position of the plurality of objects as the pitching-dependent correction amount.
More preferably, the correction means executes the correction when the average value is larger than a predetermined threshold value.
According to this preferred embodiment, when the average value of the amounts of displacement in position of a plurality of objects are large, it is presumed that amounts of displacement in position are not caused by other factors (i.e. traveling of the vehicle or movement of the objects in the real space) than the pitching motion because a displacement in position caused by the other factors is very small compared with amounts of displacement in position caused by the pitching motion, and hence this construction of the preferred embodiment makes it possible to obtain an effective pitching-dependent correction amount by a simple construction.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.